Cadillac Owners Forum banner

Changed engine ground wire, no power. 02 DTS

4186 Views 20 Replies 6 Participants Last post by  Submariner409
So I had some issues with my dash doing crazy things, things turning off while driving. Discovered that in addition to a new battery, I needed a new engine ground wire. Replaced those both, now I have no power to the dash/ignition. Bolts to the ground wire are both tight and so is the battery. To test I had ground, I used a jumper pack from pos jump point on the front fuse box to the strut bolt, where I've always jumped from. With the broken ground wire, it would not work at all unless I hooked ground to the engine directly. Now it has strong connection and sparks when jumping, but the ignition has no power without the jumper. When the wire was broken, the dash would at least come on and read some voltage. The only thing different between that and this is I have the radiator fans both unhooked so I can make sure everything is good before I put everything back together. Anyone have any idea why the power is not going from the rear battery area to the front?
1 - 6 of 21 Posts
Okay, I know it sounds confusing. I was trying to say that with the old ground cable broken, using the jumper the same way I always do would result in no ignition, but dash had power. After placing the new ground wire, I can use the jumper to get the car started from normal locations. However, it does not seem like power from the rear, where the battery is, is reaching to the front, where the fuse box is. Also now the dash gets no power without the jumper pack, with the new ground cable installed.

I bought a new multimeter but I don't really know how to use it, so where do I test and what kind of readings/ranges am I looking for? My guess is should be 12-14v from front fuse box panel to strut bolt ground is the ideal.
Well guys, I'm not sure if I'm using the meter wrong, or what, but I tried probing battery itself, negative to frame cable, tried alternator to frame newly replaced cable, and I just wasn't getting much of anything or numbers jumped. The important part is that for the hell of it, I jumped it, and drove it around the block. It drove! The dashboard voltmeter reads anywhere from 15-14.5V, barely went below 15 which doesn't sound right since I had a trickle charger on the new battery all night. 14+ volts means alternator is charging, right? Fresh battery should read 12ish on the dash?
A "12 Volt" automotive lead-acid battery should show 12.6 Volts, fully charged and disconnected from anything for a half hour.

That same battery, in the car, should show 12.4 - 12.6 at Key: ON and will allow a system charging voltage of 14 - 15.2 Volts, depending on battery condition. If, after startup, system voltage goes to 14.8 - 15.2 it will stay there for some length of time then, as the battery comes back up to full charge, ramp down to 14.2 to 14.6 Volts and stay there. Amperage, which you cannot see, will vary as the state of the electrical loads changes.

After 2005/2006 the charging specifications are much more dynamic so the DIC will show a much greater voltage spread when driving.

Negative terminal to frame is ground to ground - no voltage will result. Red = positive = +, so + to ground will show system (not necessarily battery) voltage - set to Volts DC.

When all else fails, read the directions ..........
Excellent explanation, as always Submariner. So you are saying 15V, while driving/running is normal "depending on battery charge", however, for a week old brand new CAT brand battery that has been fully topped off by a trickle charger nearly nightly since it was bought, 15V seems high, does it not?

My trashed walmart battery ran normally around mid 14's as you'd stated. The CAT brand batteries seem to be the best you can buy here, as he said they have more plates in them. I know they last much better in -40F weather in machinery out here. Otherwise it's a normal lead acid battery as far as I can tell. Same group size I had in there before, vented, just has top and side posts. Any chance 15V is because of a different brand of battery?
Automobile charging systems take into account the average sensed internal battery resistance: a dead battery looks like a short to ground - little or no internal resistance. A fully charged battery has a high internal resistance - that fully charged value can vary depending on battery construction.

That resistance value will vary the charging rate for both voltage and amperage.

What is the running system voltage after 50 - 75 miles on the Interstate ? BatteryMinder notwithstanding.......... My STS sits in the garage with a BatteryMinder connected at all times - 13.2 Volts - and when we disconnect, start up, and head for a 120 mile round trip lunch the DIC voltage is 14.4 - 14.6 each time.

EDIT: DO NOT, ever, use an old ferroresonant "trickle charger" on a battery. The new "smart" chargers are just perfect - but an old ferroresonant hummer will kill a battery in short order if it is left attached and turned on.
I had the battery and alternator tested at Oreilleys after work, all checked out okay. After driving from work to there to walmart to home, the voltage was almost as low as 14. It's just weird to me it ramps down so much after driving. To me, that seems like it needed a considerable charge.

The trickle charger I use is this one ( because it's cheap, "smart", seems to have a lot of protections against stuff, and the quick disconnect is handy. I have it wired through the pass through in the backseat to the battery and out the trunk so I just plug it in. Seems to be very waterproof too. I had it in snow half the winter hanging on a post until it fell down and got buried. Plus it has a variable charge that goes from full charge down to trickle when it's done. Seems to work nicely for the price.
Ramping down to 14 volts is normal.
From 15, though? If the battery is fully charged and brand new, it should start out near that, right? Not end near 14 after a long drive?
1 - 6 of 21 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.